Apparatus for producing and manipulating plasmas



1o sheets-sheet 1 S. A. COLGATE ETAL APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS FIG.

F l G 3 INVENTORS. STIRLING A. COLGATE JOHN P FERGUSON BY HAROLD P FURTH ROBER. WRIGHT W4' July 26, 1960 Filed June 16, 1958 FIG. 2.

ATTORNEY.

July 26, 1960 s. A. coLGATE ET AL APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS Filed June 16. 1958 l0 Sheets-Sheet 2 63 5s el 66 64 68 POWER TT SUPPLY @59 V 70 69 L76 L62 54 53 7/ 67] 56 57 52 I 78 A L POWER I 'n SUPPLY ,8j/83J L5] f77 V82 PULsER PULsER FIG. 4.

l 73 [74 Y PULSE TIME 79 TIMEr PULSER INITIATOR DELAY I DELAY LARGE E =I.O '6 MEDlUM e =o.|-

SMALL e' =0.0I I4 A Hz I2 t DATA FOR I|z a J9 cuRvEs w TAKEN AT 31.4. SEC (D '0 @s E 8 Jg; 4 FIG. 5.

a: 3 IN s 2 INNER wALL OF lNsuL TOR cb I/ A I /INNER WALL OF CONDUCTOR, c =I.0 2 I L/-INNER wALL OF coNDucToR, e'=o.|

\`\\I -f-INNER WALL OF CONDUCTOR, E =0.0I

I l I l I I STABILIZED PINCH AXIAL FIELD DISTRIBUTION BY AS A FUNCTION OF INSULATOR THICKNESS, e

7 8 INVENTORS.

STlRL/NG A. COLGATE JOHN P FERGLso/v HAROLD E FURTH ROBERT E. WRIGHT ra-.4 4.4M

ATTORNEY.

HZ, KILOGAUSS July 26, 1960 s. A. coLGArE ETAT. 2,946,914

APPARATUS RoR PRonucING AND NANIPULATING RLAsMAs Filed June 16, 1958 10 Sheets-Sheet 3 DATA FOR H a J |2^ Z 9 cuRvEs TAKEN 'o H9 AT 5 s c Tol* E m a- 3.. w HZ n: O sl- 2- 1' 4 E J9 x 4- o U 2- 1 INNER wALL oF 2` /lsuLAToR o \.l

o I l l I l l l l o 2 s 4 o 2 4 s a To l2 RADIUS, CM TIME, p. SEC

STABILIZED PINCH `AXIAL FIELD DISTRIBUTION FOR OSCILLATING Hz FIG. |4-

|2 DATA FoR H, ad@ |2 L. cuRvEs TAKEN Q g Hz AT 4,usEc |o Hl9 3 8- n: 4- D 8- 'L3 r (D et zg e- 'E Je g 4- 4 o 4- Q, INNER wALL oF H2 2' /NsULAToR 2- o I o I J l l o 2 3 4 2 o 2- 4 s a To RADIUS, CM TIME, ,A SEC STABILIZED PINCH AXIAL FIELD DISTRIBUTION FOR SELF-PROGRAMMED Hz INVENTORS; F1617.

STIHL/NG A. COLGATE JOHN I? FERGUSON BY HAROLD P FuRrH ROBERT E. WRIGHT /fm/W w ATTORNEY.

July 26, 1960 s. A. coLGATE ETAL APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS Filed June 16, 1958 10 Sheets-Sheet 4 NKT SCREW DYNAMIC PINCH DISTRIBUTION FIG. 9.

.m 6 rl, IJ H 7 2 H 9 H f H A \.,J M- a/ f m M l 1 u U... lo w FIG. IO.

FIG. /l.

N T wOHM vr.. TOSTI N NCWRR R E T WGFRE A N. T. MR/J RNOE [HRB TOAO SJHRW Y B July 26, 1960 vs. A. coLGA'rE Erm. 2,946,914

APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS Filed June 16, 1958 10 Sheets-Sheet 5 APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS l0 Sheets-Sheet 6 Filed June 16, 1958 INVENTORS. ST/RLING A. COLGATE JOHN l? FERGUSON HAROLD l? FURTH ROBERT E. WRIGHT ATTORNEY.

July 26, 1960 s. A. coLGATE ETAL l 2,946,914

APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS Filed June 16, 1958 10 Sheets-Sheet 7 TIME, ,L sEc I4 Kv 100,;02

FIG. I8.

AI-IIN LWd TIME, lu, SEC I4 KV lOOIu. D2

FIG. I7.

INVENTORS; STIRLING A. COLGATE JOHN F? FERGUSON BY HAROLD I? FuRrH ROBERT E. WRIGHT ATTORNEY.

July 26, 1960 s. A. coLGATE ET AL 2,946,914

APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS 10 Sheets-Sheet 8 Filed June 16, 1958 H CH Z 268 TRIGGER CROWBAR y P N PROGRAM PULSER PULSER PULSER PULSER 264 252 MULTIPLE NMEy CHANNEL TIME TIME PULSER DELAY DELAY DELAY. 4o-

30'- 0 EXPERIMENTAL POINTS F G. I9.

N I v INVENTORS.

y STIRLING A. COLGATE JOHN F. FERGUSON 0 0.2 0.4 R O-S 0.8 |.O BY HAROLD P FUR-TH l ROBERT E. WRIGHT -W-WM ATTORNEY.,

July 26, 1960 s. A. coLGATE ETA. 2,946,914

APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS Filed June 16, 1958 10 Sheets-Sheet 9 INVENTORS. STlRL/NG A. COLGATE JOHN E FERGUSON BY HAROLD P FURTH ROBERT E. WRIGHT ATTORNEY.

S. A. COLGATE ETAL July 26, 1960 APPARATUS FOR PRODUCING AND MANIPULATING PLASMAS Filed June 16. 1958 l0 Sheets-Sheet 10 s. R o @N @i mw @E vm w v V m E28 im .NQ 10N E208 im .No 10N Ewm 1m .610m E233@ OOQ Eumaow Oom. Eowaow OOm zwt N1 zmmt N1 zmixm N:

ATTORNEY.

2,946,914 Patented July 26, 1960 United Safes` .Paef m@ APPARATUS FOR PRODCING AND MANIPULATING PLASMAS Stirling A. Colgate, Livermore, John P. Ferguson, Los Altos, Harold P. Furth, Berkeley, and Robert E. Wright, Hayward, Calif., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed June 16, 1958, Ser. No. 742,445 17 Claims. (Cl. 313-231) various spectrographic operations or to simulate the effect of high temperature effects such as Vthose whichhigh speed missiles undergo in transit through the atmosphere. Moreover, plasmas of certain light elements, i.e., D, T, He3, etc., constitute controlled thermonuclear reaction media and are produced in a wide variety of fusion reactors employing magnetic containment elds whereby energetic particles, heat, radiation and other useful products are obtained. Small compact neutron sources mayalso be provided which produce neutrons by DD reactions in a plasma.

Thermonuclear reactors employing the so-called pincheiect have been widely usedand publicized to a greater extent than other systems in the'pa's't. Many of such reactors have various features in common since they. are concerned with the production, manipulation and utilization of a thermonuclear reaction plasma in magnetic eld configurations which have various Vcharacteristics in common. Linear pinch type apparatus provides a very simple means for studying the behavior of plasmas; however, it is generally believed that the toro'idal type are more applicable for large-scale operations due to reduction of end losses. Experience with simple pinch apparatus indicates that various instabilities occur at early stages in the production of a pinch discharge or plasma which disrupt the plasma and prevent the attainment of the stable high temperature plasmas which are necessary to obtain stable and high efiiciency operation of the apparatus.

Considerable progress has been made towards stabilizing the pinch discharge by providing accessory magnetic fields which reduce or eliminate one or more of the instabilities which occur in such discharges. One of the more successful methods of stabilization is that disclosed in the copending application of Stirling A. Colgate et al., Serial No. 685,771, together with an exhaustive analysis of such instabilities and the conditions necessary to obtain a thermonuclear reaction in such a reactor, which'disclosure is incorporated herein by reference. VSuch stabilization is effected by including an internallongitudinal or axial magnetic eld, Hz, in the plasma column and operating within specified regions of stability as well as employing an external stabilizing shell to which ux lines couple.

In order to obtain most eiective stabilization the zone between the entrapped magnetic stabilizing eld, HZ, and the azimuthal field, H0, must be thin compared to the radius of the plasma since the existence of a small amount of Hz iield external of the plasma can exert a very strong de-stabilizing iniluence. 'I'he establishment of a sharp boundary zone has therefore been sought and Yobtained with a degree of success for certain types of discharges; however, various linear and toroidal pinch experiments have yielded magnetic eld Vdistributions which are so diffuse that neither practical nor theoretical stability can be shown. It was originally thought that the resistive diffusion ofthe orthogonal iields, HZ and H0, into each other would be a limiting factor in sharp boundary formation but that an adequately sharp eld Vdistribution would be obtained withla suiciently rapid rate of pinch formation, i.e., attainment of high plasmaconductivity.- This condition is necessary but not completely suicient to obtain consistently'sharp eld separations or boundaries.

Ordinarily, the region between the insulating vacuum chamber wall and the pinch discharge proper has been considered to be a vacuumreld region; however, 4this region is not actually a vacuum` since a gasV such as deuterium is boiled off of the walls y-by the heat of pinch formation and occupies the indicated region. Since this gas is easily ionizedand may have Ya density in excess of 1013 electrons per cc., the region may have aconductivity comparable to that existing Ywithin the epinch itself. This externalplasma may even b'e'hotter' than plasma inside the pinch if diiusionrheating occurs. The external'plasma conductivity will, in general, be suciently great to entrapany residual Hz ilux external of the pinch proper and prevent uniform distribution thereof within the tube.

In accordance with the present invention the `boundary value of the axial eld, HZ, at the insulating Wallis caused to be reduced to a zero value or to a value whichis an appropriately programmed function of compression whereby the boundary between the HZ fields Within a high conductivity pinch and the Hs field external thereto is made sharp and the pinch is stabilized. Other stabilizing eiects may also be obtained by appropriate programming and utilization of the external conductivity of the vplasma as disclosed hereinafter. Ordinarily the present method of stabilizing a plasma will be applied to a high conductivity discharge so that the added stabilizingvetfect due to controlled diffusion broadening may be utilized. l

Accordingly, it is an object of the invention to provide methods and apparatus for producing stabilized hightemperature plasmas. Y

Another object of the invention is to provide methods and apparatus for producing stabilized pinch discharges.

Still another object of the invention is toy provide methods and apparatus wherein the external conductivity of a pinch discharge is utilized to provide magnetic eld distributions which stabilize such discharges.

A further object ofthe invention is to provide methods and apparatus wherein the axial eld HZ external to va stabilized pinch discharge is reduced to a negligible value so as to provide a sharp stabilizing boundary between internal Hz and external H, fields of the discharge.

A still further object of the invention is to provide methods and apparatus wherein the boundary value at the insulating wall of the axial iield, Hz, is reduced to a negligible value or to a value which is an appropriately programmed function of compression of the plasma to obtain stabilization and create other beneiicial eiects in the plasma. A

Other objects and advantages ofthe invention will become apparent by consideration of the following description taken in conjunction with the accompanying drawings of which: 4

Figure l is a simplified graphical representation of a side wall portion of a pinch tube illustrating a current distribution in a pinch discharge;` v

Figure 2 is a vertical cross-sectional view of a stabilized linear pinch tube including magnetic field producing means for operation in accordance with the invention;

Figure 3 is a cross-sectional View of the tip of a probe employed to measure eld distributions;

Figure 4 is a schematic simplified Wiring diagram for operating the device of Figure 2; Y

Figure 5 is a plot of a stabilized pinch axial field distribution as a function of insulator thickness e;

Figure 6 is a graphical illustration of a stabilized axial field distribution obtained with an oscillating Hz eld;

Figure 7'is a graphical illustration of a stabilized pinch axial field distribution employing a self-programmed HZ circuit arrangement;

Figure 8 is a graphical representation of the field distribution with uniform Hz eld external to a standard dynamic pinch discharge;

Figure 9 is a graphical representation of the screw dynamic pinch distribution under specified conditions;

Figure 10 is a vertical cross-sectional View of a screw dynamic pinch tube apparatus;

Figure 11 is an idealized representation of the magnetic field configuration in the plasma within the tube of Figure 10;

Figure 12 is an idealized representation indicating electrical currents, magnetic fields and field pickup loops employed in various screw dynamic pinch experiments;

Figure 13 illustrates typical oscilloscopic traces of various measurements made on a screw dynamic pinch in deuterium;

Figure 14 illustrates typical oscilloscopio traces of various measurements of a screw dynamic pinch in hydrogen;

Figure 15 illustrates the effect of :pz leakage flux on external 1pz ux on development of an m=1 instability in the pinch;

Figure 16 illustrates the behavior of the HZ field inside the return conductor yet outside the pinch in the course of a screw dynamic pinch;

Figure 17 is a graphical illustration of the correlation of neutron outputs with current application to the screw dynamic pinch tube;

Figure 18 is a graphical illustration correlating neutron output with field behavior in a screw dynamic pinch;

Figure 19 is a plot of the actual and the theoretical HZ field distribution in screw dynamic pinch;

Figure 20 is a plan view with the external conducting shell broken away of a toroidal pinch tube apparatus termed gamma pinch which is adapted for operation in accordance with the invention;

Figure 21 is a vertical cross-sectional view along the plane 21-21 of the apparatus of Figure 20;

Figure 22 is a vertical cross-sectional view along plane 22-22 of the apparatus of Figure 20;

Figure 23 is a schematic wiring diagram of the electrical circuitry employed with the apparatus of Figure 20;

Figure 24 is a graphical illustration of results employing the gamma toroidal pinch without programmed HZ field;

Figure 25 is a graphical illustration of results employing the gamma toroidal pinch with external HZ field programmed or reduced to about zero at the tube wall; and

Figure 26 is a graphical illustration of results employing the gamma toroidal pinch with external HZ reduced to negative value at the tube wall.

The conditions necessary for producing a thermonuclear reaction are quite well known and are disclosed in detail in the aforesaid copending application together with operating parameters of fusion reactors summarized hereinafter. In order to obtain such a reaction it is merely necessary to contain an appropriate volume of thermonuclear fuel at a high temperature whereby the fusion reaction occurs between colliding nuclei. Kinetic temperatures of the order of l()8 degrees Kelvin are necessary. To obtain a self-sustaining reaction a minimum volume of gas at a correlative density and pressure such that the energy produced in the system equals or exceeds the energy loss is required. However, such a reactor may be operated with a negative power balance if it is desired to employ the charged particle, radiation, plasma or other product for purposes other than power production. In thermonuclear reactions deuterium and tritium constitute preferred fuels which are subjected to I(DD` and TD) reactions for which 27 kev. is the ideal ignition temperature of the former and 3.4 kev. is the ideal ignition for a 50-50 mixture of the latter. These are the minimum temperatures at which the indicated reactions can be self-sustaining and an adequate excess thereover is necessary for net power output gain over input energy.

The basic mechanism whereby the pinch effect operates to contain a plasma is dependent upon the magnetic selfconstricting or containment field which is produced by an electrical current flowing ina plasma, i.e., a highly or fully ionized gas. With space charge neutralization existing in the gas, mutual repulsion by like charges does not occur and the full compression effect of the generated field effects causes the charged particles to converge in increasing densities toward the center of the current distribution. To a first approximation the current magnitude required to produce such an effect is determined by the equation 12:3.2 X107NT where I=current in amperes N :total particles per unit length of current path T=temperature in kev.

Two types of classical pinch apparatus are in general use, i.e., linear and toroidal. In the former an electrical current discharge of appropriate magnitude is produced in an elongated insulating housing or tube containing, e.g., deuterium at reduced pressure by applying a high voltage across spaced electrodes therein. In the second type a toroidal housing is employed and the current is induced to flow in a preionized gas by an externally coupled winding which is usually a single turn primary. In modest size apparatus electrical currents of the order of 105 to 106 amperes or more may be utilized producing a constricting effect upon both electrons and ions as well as causing collisions therebetween which increase the temperature of the gas eventually resulting in temperature and density conditions Whereat one of the foregoing nuclear reactions may occur. For certain other purposes lower temperatures and short containment times may be utilized.

In the operation of such classical pinch type apparatus it was found that the pinched or constricted discharge was not stable with reference to lateral displacement due to the rapid onset of an instability commonly referred to as the kink or Kruskal-Schwarzschild instability. As disclosed in detail in the aforesaid copending application a great increase in stability results by inclusion of a longitudinal magnetic field within the constricted plasma and by employing a conductive metal shell around the plasma. In general, for stability, the 4internal stabilizing field, Hz, must be equal to the self-constricting eld, HD. (The foregoing quantities are referred to as BZ and B(9 in the aforesaid application.) For stabilization against sausage instability more than half of the internal pressure of the pinch must be due to included Hz field. If longitudinal field can be excluded from the region external to the pinch, the pinch may be stable at radial cornpressions up to 5:1 for null plasma pressure and at compressions up to 2.5 :1 for a plasma pressure equal to half of the pinch pressure. However, if I-IZ external of the pinch is as much as 1/2 of the pinch eld strength at the plasma surface the pinch becomes unstable at 1.8:1 compression even at null plasma pressure.

Certain other considerations as to containment, heating, apparatus details, circuits, etc. relating to the design and construction of the reactors disclosed in the aforesaid copendingl application are relevant to the construction of reactors in accordance with the present invention and such disclosure S therefore included by reference.

- s noted above the external plasma conductivityswill; in general, be suiciently high to entrap any Hz field external of the pinch and prevent uniform distribution within the tube. The exact shape of the HZ distribution is determined by the variation ofthe boundary volume of HZ at the tube wall as a function of compression. Without added HZ the variation in time of the boundary value of HZ will depend on the constant 6 which is the ratio of the internal diameter of the insulating pinch tube to internal diameter of the Hz generating coil or of a conductive shell surrounding the pinch tube. This region normally serves as a reservoir of Hz ux which is gradually depleted during pinch compression as by move,- ment inwardly.

The significant effect which an arbitrarily broad current distribution that results from the assumption of perfect conductivity everywhere within the walls can exert in the pinch boundary formation process is easily demonstrated. In practice perfect conductivity is quite closely approximated with high temperature plasmas. Consider the simplied graphical representation of a sidewall portion of the pinch tube illustrated in Figure l of the drawing with an external conducting (metal) wall at x=e and an insulator extending from x=e to x=0. As-in an actual pinch discharge a perfectly conducting pressureless plasma is continuously generated at the insulating wall, x=0, e.g., by ionization of neutral gas boiling off or outgassing from the insulator surface due to the effects of the pinch discharge. This conductive plasma is continuously pulled away Ifrom the wall and intothe tube as constriction of the plasma proceeds. Consequently, perfect conductivity exists everywhere inwardly from the Wall of the tube. Considering e small compared to the radius R=1 of the pinch tube, for all deformations of the order of e, radial convergence can be neglected and plane-parallel geometry. assumed. The effects of particle inertia and pressure can be neglected since a small and slow compression is considered.

With the stabilized pinch method of operation, the entire region inwardly of the conducting wall is initially filled with a uniform longitudinal magnetic ield Hm and no current ows within the plasma. As the axial electric eld is applied an axial (pinch) current begins to flow along the plasma surface x= and is returned back along a conductor disposed around the tube wall. Simultaneously an H9 (pinch) magnetic field is generatedin the insulating space -eSxSQ In order that the magnetic field pressure in this space may not rise and cause imbalance across the plasma surface, the plasma must move inwardly and away from the insulating wall surface. The rate of the indicated plasma movement can be related to the rate of rise of the H(9 field which itself, of course, is directly dependent upon the currentrproduced by the applied axial electric iield. Time-dependence of phenomena is not of direct interest in the present consideration since it is the shape of successive equilibrium coniigurations which are of primary interest and these are not dependent on the rate of formation.

When plasma near the tube wall is caused to drift inwardly the plasma everywhere from x=0 to x= must drift by exactly the same amount otherwise the magnetic eld would be compressed locally which would be incompatible with pressure balance. Therefore, inwardly from the original plasma surface, the HZ distribution remains completely unchanged. Outwardly from the plasma surface a mixed He--Hz distribution exists and is to be calculated. Once an HZ value is determined at a given plasma point the He value is fixed as indicated by the following equation:

Furthermore both the HZ and Ha values must remain constant at a given plasma point since there is no compression, only drift, and no diffusion. 'Ihus the entire distribution can be characterized by specifying Hz as a` distribution'is (In =geen@:Kaarsje which may be solved to give l i f;

where the boundary condition H :H21 at x=s has also been used. The distribution ofthe H, then follows as and the current density is given by the distribution illnstratedinfFigure 1 Vis Vobtained: and indicates the manner in which a current distributionA having a width we can be formed in a plasma despite the assumption of perfect conductivity. If the resistive diffusion elfect is included the resulting distribution Will'always. be broader; however, itisimportant to be Ware that the linal pinch distribution ispr'oduced` by'two separable physical phenomena. The resistive diffusion is determined by electrical conductivity, dimension and, time whereas the .external Aconductivity effect depends .upon the particular boundary value of Hz as a function of4 compression.

The regime just calculated was determined by an initially given value of external axial eld ux equalto e Zi. Operations need not be limited to this boundary condition but HZ at x=0 can be programmed or manipulated to be any arbitrary function of compression or of H, so that more,favorableand highlyinterestingu distributions can be entrapped or produced. The infinitely sharp boundary case is formed by a program such that the HZ line of force at the insulator wall (J'c=0) remains stationary while HZ2 pressure is replaced with H2 pressure, i .e., the boundary condition to be maintained in order to generate the innitely sharp'boundary entrapped wherein HZ is decreased-from the initial value H21 to some desired final Value Hzf which may be for example zero or negative. Other cases ofvgreat importance involve the entrapment of magnetic iields which represent complex'Hz functions such as multiple oscillations complete eld reversal. In practice the'desired distributions are obtained by"appropriatelyl applying magnetic lields from sources which are controlled or programmed where p is the plasma pressure and n its density. The first two equations (X and DG) may be combined to give H,l l (XV) V at c? am@ H@ (XVI) --rcsrw since the only non-vanishing component of v is the radial velocity v. It is helpful to define the quantities (XVII) qsFL'HzTldT,

(XVIII) 4 O'Hgdr1 Eliminating v from Equations XV and XVI, one obtains simply @I @n gz ne:

which implies that 4, can be expressed as a function of pz only.

By differentiating Equation XX with respect to r, one can show that (XIX) (XXI) HFMHZ where is also a function of pz only. Equation XXI states that if one follows a particular plasma point (that is, a point of constant zpz) during compression, then the slope which may be combined with Equation XV to give i t '8 where i i (XXIV) N=f'm-1dr,

0 It follows that N can'be expressed as .'a`function of gp; only. The analogue of EquationrXXI` is (X'XV) n=gHz where represents a function of pz only.- b

The infinite electrical conductivity plasmaund'er con-v sideraton is naturally one of negligible thermal conductivity. Thus each innitesimal plasma volume is com-- pressed adiabatically, andthe 'quantity'CinrEquation XIII must be a constant at aparticular plasmajnoiut. Consequently C can be expressed asa function of (bz only: The pressure balance EquationXII can now be written (XXVII) dr (XXVIII) r d'r d1' r dr from which (XXIX) and the primes `denote diierentiation with respect torpz. When the plasma region under consideration is that external to the pinch proper, the particle pressure can be (l-faufsgz) where at sorne radius, such as r=0. The magnitude of HZ at such a point serves to label the stage of compression or expansion and so takes the place of time as historical parameter. l

An ordinary second-order differential equation of the type of Equation XXIX or XXX is easy to solve numerically, provided that p., g and C are known as functions of qz over the interesting range of bz. Thus it is always possible to begin with some distribution over the pinch tube and deduce all earlier stages, at least in the ideal limit of innite conductivity. This is done by recording (pz, u, g, and C as functions of r for the distribution in question and combining thesedata. inthe formof tabulations of p, g and C vs. pz. All four `ofthese variables will become different functions of fr at different stages of compression, but theY same functional dependence on pz is maintained. It therefore merely remains to calculate specific distributions for selected boundary values HZ, by means of Equation XXIX or XXX.`

A more difficult problem is to begin with a known distribution plus an extra boundary condition at the pinch tube wall, and to calculate the distribution ofl subsequent stages of compression. If p20 is the z-flux initially in eluded in the tube, then ,u and g are known as functions of pz for Oqzpzo. For bz z0 oneA cannot simply use Equation XXIX or XXX, but must alsomake use of the information contained in the extra boundary condition.

As an example, consider the problem of'compressing the null-, uniform HZ distribution which was treated earlier in the plane approximation. Let the insulating tube thickness be e and let v where the tube inside radius is taken as unity. vThe zflux conservation requires that at r=1 One must now proceed as in the case of a partial diiferential equation, by calculating the distributionmat each stage of compression with the aid of the distribution at the immediately preceding stage. For Oqbzpzo the calculation is trivial, since a remains identically zero in this interval. Let us suppose a iield distribution at some nth stage of compression such that r=1, pz=q1m pz0.v Then for all subsequent stages the field distribution can at least be calculated in the interval fpxopzpm by means of Equation XXX. At the (n|l)th compression stage, the condition Z=Zn is necessarily reached somewhat short of r=l. At this point vthe extra boundary condition given by Equation XXXI is invoked to extend the pz vs. r curve to a new limiting value pmu atv r=1.

Apparatus in which a stabilized pinch discharge may be produced in accordance with the teachings of the invention may be of the linear, toroidal ormore complex tubular pinch tube types. In general, such apparatus will therefore include pinch discharge tube means, i.e., a tubular housing formed of a magnetic ield permeable insulator material of either a linear cylindrical or generally toroidal configuration and provided with evacuation and gas supply means for introducing the gaseous atmosphere in which the discharge is to be produced. rIn the linear pinch tube device, electrical current supply .means are provided for generating a linear current dischargeY between electrodes longitudinally within the tube and in the toroidal device the electrical supply means is coupled inductively through single turn solenoid means to obtain the discharge. Means including a solenoid or other current carrying means are provided for supplying a stabilizing HZ within the tube in a manner similar to that dis closed in the aforesaid application; however, in accordance with the present invention the arrangement of such solenoid or of the current source employed to supply the energizing current to such solenoid is modified yso that the Hz iield is either an appropriately-programmed or a self-programmed function of compression whereby a sharply defined boundary, otherwise stabilized boundary or any desired selectivelystabilized boundary is produced in the pinch discharge. Alternatively, a separate programmed Hz eld solenoid may be employed. Ordinarily, the device will also include means for inducing initial ionization of the gas to facilitate or initiate formation of the discharge especially if rapid yformation and compression of the plasma is desired, v v l Y The linear pinch tube apparatus illustrated in Fig.21

(XXXI) festem lb of the drawing Ymay vbe incorporatedfin appropriate circuits and operated in accordancei'with'the foregoing principles. Apparatus10 is constructed with an elongated charge is formed. The lower electrode k13 is extended downwardly providing a neck portion 14 and is provided Y with a flanged portion 16 having 4an outwardly projecting terminal 17 to which one conductor of transmission line 18 is coupled as disclosed below. Ashoulder 19 above neck V14 supports gasket Ztl'which in turnvprovidessupport for the lower end of tube 11. The electrode 12 Vis Vprovided Ywith a flanged portion 25 extending outwardly electrode 12 and extends in spaced concentric relation along tube 11 to terminate in flange 23 which is spaced from' lower electrode ange16 by means of insulator sheet 24. Flange 23 is provided with outwardly projecting terminalV 26 to which the second conductor of transmission 'line.18 is connected completing the electrical discharge circuit of the apparatus 10.

YA fitting 27 is yprovided in electrode 12 for coupling to evacuation and gas supply means (not shown) for removing extraneous atmospheres and introducing a desired atmosphere, eg., deuterium or deuteriumLtritium mixtures. A spark plug type trigger 28, mounted in a perforation in electrode 12 comprising a tungsten elec trode 29 contained in insulating sheath .30 terminating at the lower face of electrode 12 and extending outwardly through vacuum seal 31, is coupled with conductor 32 to an external electrical p'ulse generator (described below). The trigger circuit is kemployed to produce initial ionizationA by discharge to electrode 12 and facilitate formation of the pinch discharge in the device. A probe 33 including an elongated quartz tube 34 sealed at the lower end is supported within a perforation formed centrally in electrode 12 by collar 36 sealed thereto which collar is in turn supported by theupper end of Sylphon ybellows 37 which is sealed at the lower end to electrode -a Vhelical conductor 43 in fiberglass cloth contact pressure laminating resin (Epon) laminate 44 is arranged concentrically about return conductor 22 in order to providev stabilizing HZ eld'as taught in the aforesaid copen'dingV application; however, as described hereinafter, such solenoidl 42 may also be excited to provide lan HZ field boundary conditionprogrammed as a function of compression. An Hzprogramming solenoid Y46 -comprising heavy braid'or strip conductor Wound on tube l1 vmay also be employed for programming the Hz field as here- 1 inafter: described. Meansformeasuring current inthe tube may be provided by disposing a solenoid 47 circumferentially oriented Within an annular space 4'8 provided between neck 1f4 of electrode'13 and flange 23. Conductors 49 led exteriorly may thenbe coupled to conventional instruments to measure the current produced therein' by changing flux fields in the region indicated.

A simpliiiedV typical circuit employed for operating the linear pinch tube .10 is schematically illustrated in Fig.

. 4of the drawing. The vbasic operating procedure re- 4stabilizing Hz -eld therein; Y T02 Previti? the. Pi??? (Qur- 11 .rent transmission line 18, which supplies .electrodes f12 and 13, is coupled across capacitor bank 51 which will, in gener-a1, comprise several high voltage condensers and switching tubes in parallel arrangement. Capacitor bank 51 is charged through a vacuum switch 52 by power sup- `ply 53. The high voltage pinch current is switched by ignitron 54 having the anode 56 coupled to one side of the transmission line and the cathode pool 57 to one side of condenser bank 51.

A sequentially timed switching arrangement may be employed to lapply the HZ exciting current to terminals .58 and 59 of solenoid 42 through transmission line 61 from a capacitor bank 62 indicated as a single condenser. Multiple ignitrons for switching capacitors 62 in a parallel arrangement corresponding to single ignitron 63 with the anode 64 coupled to one terminal of bank 62 and cathode pool 66 to one conductor of the transmission line 61 is employed for such switching. The second conductor of the line 61 is coupled to the second terminal of the condenser bank. Power from supply 67 isapplied through vacuum switch 68 to charge bank 62. A

-second ignitron y69 with the anode 71 coupled to second conductor of line 61 and cathode pool 70 coupled to the first conductor of line 61 is triggered as described below to cause crow-barring or shorting of solenoid 42 and exponential decay of the field following energization by bank 62.

Variable sequential operation of the foregoing circuits is obtained as by applying an initiating pulse from a multiple channel pulse initiator unit 72 through a Variable time delay unit 73 and pulser 74 to igniter 76 of ignitron 63 causing bank 62 to discharge through solenoid 42. At a selected time a pulse supplied by another channel of delay unit 73 is subsequently applied through pulser 77 to igniter 78 of ignitron 69 causing the aforementioned crow-barring action and establishment of the initial Hz eld at the desired level. A simultaneous initiating pulse is applied from initiator 72 through a channel of variable time delay unit 79 to pulser 81 which applies an ionizing pulse between electrode 29 of trigger 2S and pinch tube electrode 12 thereby providing favorable ionized gas conditions for the pinch discharge to occur between the pinch tube electrodes 12 and 13. At a time determined by the setting of a second channel in unit 79 shortly thereafter a pulse is applied through pulser 82 to igniter 83 of ignitron to cause discharge of bank 51 between electrodes 12 and 13 providing the pinch discharge in tube 11 which traps the initial stabilizing field Hz therein.

Various experiments were performed employing the basic apparatus and circuitry described in the foregoing with specific structural details, dimensions, and specifications noted hereinafter.

Tube 11 2.718 inches I.D.

Elec. 12--13 16.875 inches spacing. Solenoid 43 170 turns No. 8 Cu Wire. Condenser bank 51 150 mfd.

Condenser bank I l0 kilovolts.

Initial field I-IZ 4600 gauss.

Initial deuterium pressure 200 microns Hg.

Results were determined for various radial positions of probe 33 with the signal being integrated with an RC circuit and then displayed on an oscilloscope screen as a function of time. Sufficient pulses were observed at each position to insure reproducibility of results. A final field plot at a given time was subsequently determined from the time history of the field at each point.

A series of determinations were made by varying the distance e between flux conserving electrode 22 and inside surface of the wall of tube 11 with the results illustrated in Fig. 6 of the drawing. The indicated values are those existing at .peak pinch current which in most cases occurred closeto 5 ltsec. after start of the pinch. The

broadening .effect on the `I-Iz distribution with increasing .insulator Ythickness .e is apparent. The width of the .field distribution in the case of the minimum insulator thickness (e=.0.0l) is obviously much greater than the espace itself so that in this instance the Width of the distribution must be governed by diffusion. However, fthis diffusiony distance is in turn considerably Vsmaller than the widthv of the distribution obtained withv the larg- Vest insulator space (5&1) so that in the latter case the distribution is governed by the wall boundary condition.

To illustrate how an arbitrary distribution can be lcreated independently controlling Hz at the Wall as a `function of H6, a fast condenser (not shown) was coupled across terminals 84 and 86 of solenoid 46 and allowed to oscillate during the rise of the H, field produced by the pinch discharge. The resultant magnetic field behavior at lthe Wall boundary |and the resultant spatial distributions of field ,and pinch current .l9 are shown in Fig. 6 of the drawing. During the formation of the pinch discharge the Hz field at the Wall started at a high value, diminishedl to zero, increased to the original value rand again diminshed to zero. The field distribution shown occurred-at 4the time Hz approached zero for the second time. It was expected that if the space external to the pinchI were conduct-ing, then the second positive peak in the HZ field would be clearly trapped in the external plasma as a peak in the spatial distribution of the Hz field. The second peak in the observed radial distribution confirms the basic -accuracy of the concept of external conductivity and the foregoing operation indicates a general method in which the field distribution can be modified or desired field distributions created by 35 -the trapping of Hz field in the external plasma.

`occurrence of the pinch. With small size apparatus such as the foregoing appropriate accessory programming circuitry is difiicult to design due to the very small time periods available; however, with large size equipment appropriate equipment controlled by current iiow or magnetic field detectors such as the solenoid 47 may be provided. The Hz programming solenoid 46 was coupled across the transmission line 18 in self-programming fashion such that some of the bank 51 current i'lows therethrough and tends to reduce the value of Hz exterior of Vfthe pinch at the wall thereby Iapproximately an accessorily programmed operation.

Results obtained by this method of operation are illusv'trated in Figure 7 of the drawing indicating the behavior of Hz at the wall as a function of time together with the HZ distribution in space. If no such energization of solenoid 46 were employed the distribution would have been identical with the case of largest e in Figure 5. The more rapid reduction in boundary value of HZ in the present instance clearly produced a narrower and improved field distribution and demonstrates the benefits which result from programming out the HZ flux external to the pinch proper to obtain the sharper Hz--H0 field separations.

In view of the foregoing field behavior, the effect of applying excess negative Hz field was investigated and it was found that by driving the HZ field strongly negative, i.e., applying a strong field having reverse orientation to initial HZ, an m=l instability is produced in such a direction that the HZ field at the center of the tube is reduced. Accordingly, this discovery provides a powerful means of modifying magnetic fields within the dis- -charge -itselfso as to` modify conditions during various A very interesting application of the concepts of the invention is demonstrated in an arrangement in which a small axial field component is trapped external to the main plasma column of a dynamic pinchY (no initial HZ iield) discharge and is compressed to high values (comparable to the primary pinch field H9). (TheV entrapped external eld suppresses the "1:0, `sausage instability and enhances the m=l, helical instability mode yielding longer containment times Aand reducing Vspuriousneutron yields from the m= mode thereby simplifying study or use of the true thermonuclear reaction occurring inthe discharge. The large non-thermonuclearyield Afrom the rapid growth of m=0 instabilities masks the true yield and the discharge breakupoat the time of the second and third magneto=hydronomic bouncesy of the dynamic pinch discharge prevents adiabatic heating with further rises in pinch currents. Since the dynamical heating may reach 200 e.v. which is only a factor of `about 2 below which thermonuclear reactions begin to occur at a substantial rate (800 e.v.) even a` slight increase in containment time would be 0f considerable merit.` g l The possibility of stabilizing a pinch hagainst vin--O instabilities by adding an external ield` has been contemplated heretofore and been considered Vimpractical due to large energy requirements. However, the value of external HZ eld necessary to materially delay breakup is equivalent to the maximum Ha pinch eld.Y Since the pinch field diminishes as l/r anditnwasassumedl that the Hz eld would be of a uniform value lfrom the insulator wall to the pinch boundary it was evident that a very large fraction of the total energy' applied to the system would be in the external Hz lield as illustrated in Figure 8 of the drawing. A pinch Aof thisconguration for a 10:1 compression ratio, ie., initial" to final radius, requires 12 times as much magnetic energy as one without HZ iield to contain a plasma under similar NKT conditions. By trapping HZ ux'in 'the external plasma and applying compression thereto to obtain the required HZ eld intensity only modest increases, eg., a factor of 1.7 in the 10:1 compression case considered below, are needed to give significantly increased containment times over the standard pinch.` With higher compression ratios the energy comparison Vbecomes veven more favorable. The new type of discharge-has been termed the screw dynamic pinc or partly stabilized pinch for reasons apparent hereinafter.

when the plasma initially leaves the walliH9=HZ when a 10:1 compression ratio occurs. The boundary value will of course modify this relation but if the simple condition Hz Y is maintained constant a simple distribution results. The distribution Values for HZ and H9 may be calculated from /.t=l0, Where r1=tube radius the screw dynamic pinch distribution of Figure 9 is-obtained. Y CalculationsV indicate that the screw dynamic pinch should be stable by Yduced by simply utilizing a standard linear pinch tube in which the Vreturn conductor is divided into insulated segments slanted along a helical path of shallow pitch. The apparatusiof Figure 2 with solenoids 42 and 46 "removed and return conductor22 modied may be so employed; however, the modified version 100 illustrated in Figure lO'of the ,drawing was employed with a modied power supply in a wide variety of operations.

' A quartz tube 101 having upper 102 and lower 103 lterminal flanges was` provided with upper 104 and lower 106 reentrant electrodes to serve as a pinch tube. Electrode 104 is provided with a flange 107 projecting outwardly and bearing on O-ring 108 resting on the upper 'facer of .tube iiange 102 for sealing. Electrode 106 is likewise provided with a ange 109 projecting outwardly and bearing on O-ring 111 resting Iagainst the lower face of tube ange 103. Flange 109 is extended in an edge area and connected to conductor 112 of a transmission line Y113 and is provided with conduit 114 leading to a gas supply system (not shown). \The outer edge of ange 107 of electrode 104 is attached to a return conductor 116 formed 'as a series of insulated braid strips 117 extending `in closely spaced helical parallel pathsA along tube 101 and terminating in a lower ring 118 employed as a terminal. Ring terminal 118 is extended as conductor 119 of transmission line 113 separated from conductor 112 by insulator 121. Upper electrode 104 is tted with conduit 122 leading to a vacuum pump system (not shown) and with a probe 123 oriented to determine I-Iz at desired llocations in tube 101 somewhat as above. A 0 oriented magnetic coil probe 124 was employed adjacent the lower side of 'llange`102 and external I-IZ oriented Iloop 126 was disposed, radially about central regions of tube 101 exteriorly of conductor 116. Loop 127 oriented coplanar with the longitudinal axis of tube 101 and disposed exteriorly of conductor 116 was used to determinewall axial iieldv flux changes. Y In the model employed in 'experiments described below, conductor 116 was formed `of 27 strips 117 and tube 101 was of 10 cm. I.D. with a 20 cm. spacing between electrodes 104 and 106. Each strip made about 1A() turn around tube 101. A spark trigger (not shown) similar to that described above was also employed. Power was applied to transmission line 11?: from a switched condenser bank somewhat as above (not shown). The condenser bank comprised 20 capacitors of 7.5 mfd. each connected 5 in a series string with 4 strings paralleled yielding 6 mfd.

.effective in a Marx type circuit. 20 kilovolt charging potential was available; however, 12 to 14 kilovolts per capacitor was used. Individual triggered air spark gaps were employed between each pair of series capacitors and the load which gaps were triggered simultaneously by simultaneous pulses applied to trigger electrodes.

With the foregoing arrangement of return conductor 116 Hz field proportional to both the pinch current and pitch angle or degree of conductor twist is generated near the tube wall. Therefore H, and HZ external of the pitch assume ia certain fixed ratio near the tube wall dependent only uponthe twist angle of return conductor 116. The field conguration illustrated in Figure 11 results from the arrangement shown. With reference to Figure 12 was measured with a current loop coupled to a current feed line,

I' measured with loop Ar126 is a measure of total axial field ilux inside l'the returnconductor 116,. Hz wall by probe 124, and Hz axial by probe 123. Gamma ray and neutron fluxes were determined with scintillation counters (not shown). The voltage across the tube 'was measured with a standard voltage dividing resistor (not shown).

Figure 13 shows typical traces of the signals of a screw dynamic pinch for 14 kV. on each capacitor (70 kv. all) and 100-micron deuterium pressure. The top trace is a long-time signal from a large (8-in. diameter) scintillation counter surrounded with additional paraiiin, located immediately against the pinch tube. The many pulses observed at 50-100 nsec., with the characteristic decay of approximately 100 Iusec., furnish unique identification of the thermal-neutron capture in hydrogen. by making observations for a long time (100 nsec.) after the pinch discharge, one cannot possibly confuse these pulses with electrical pickup signals. Figure 14 shows the same trace for hydrogen With the large resultant decrease in neutron yield. The slight residual deuterium gives rise to a few neutrons. The

ticularly, in accordance with theory, as shown by the following equations:

(XXXII) dH. Wann am 1 r1. dt n 10 dt 10 5R t Therefore dI 2 -B (XXXIII) d. R X @X10 dt 10 5R If R=7 cm. and dl/ dz=2 1011 amp/sec. at first bounce,

(XXXIV) 3?: 1.s5 1o3 vous This is in good agreement with the measured values just before first bounce. A short time later, however, the dez/dt signal increases by roughly 5 times. The signal is interpreted as the growth of the m=1 corkscrew instability.

If the total current remains roughly constant (the dl/ dt signal being less than at the start of the pinch), then .the only way for the ez ux to change by a large factor is by means of a change in the current configuration. The return braid conductors are fixed in space, so that the only part of the current circuit that can move through large dimensions within the small time available is the pinch configuration itself. In order :that the pinch give rise to a change in the tbz flux external to the tube, the current cf the pinch must wrap up into a helix, in such a direction as to give rise to a negative HZ outside the pinch and inside the braid.' The leakage of a small fraction of this reverse l-IZ field through the slots in the braid gives rise to the observed large positive dQSZ/dr external signal. Figure l2 shows the helical pinch conguration and the leakage iiux linking the single-turn loop with the resultant dqbZ/dt.

The bottom trace of Figure l5 shows the elect of this tbz leakage ux on the external rp, flux. Note that there never can be any H-e iield outside the return Vconductor unless there exists an asymmetry in the pinch current pattern. When the pinch twists up into an m=l mode, the result-ant leakage of 4:2 ux between the braid should force a fz component to flow externally, with a resultant dbH/dt signal. The experimentally observed signal is,A in fact, roughly zero until the time of the mi=1^helical instability growth, at which time it increases by at least a factor of 10 (see Figure 15). This confirms the concept of the instability distortion of the currentpath.

Figure 16 shows the Hz eld (integrated current loop) inside the braid return conductor, yet outside the pinch. At the time of the m=1 helical instabilityIthe external boundary value of Hz is driven violently negative, in agreement with the expected behavior.

The fast time behavior of the scintillation-counter signal with one inch of lead Ishielding is shown in Figure 17. The rst peak corresponds to the time of application of voltage and therefore the radiation is probably due to a direct acceleration process. Figure 18 shows the same signal with an additional one inch of lead shielding. The rst peak is attenuated by a large factor indicating gamma or X-rays, whereas the second peak is not affected and is therefore associated with the already-verified neutrons. As additional confirmation, the rst peak is independent of whether hydrogen or deuterium is used, but the second peak occurs only with deuterium.

The yield occurred only with the marked appearance of the m`=1 instability. A large instability gave a large yield, etc. The yield was very sensitive to voltage (on the order of the fifth power), and inversely sensitive to the pressure (on the order of the third power), for pressures of 50 microns and above. Below this pressure a dynamic pinch did not form.

It is evident that the neutrons are associated with an instability growth, and so, without further evidence, it is assumed that they are not thermonuclear in origin. The high electric field accelerating mechanism of the m=0 instability growth does not apply in the case of m=`1 instability. The amount of magnetic flux that the ions must cross, turn to turn, is too great in terms of possible electric fields, and so some other accelerating mechanism must be invoked for a non-thermonuclear origin, such as a Fermi mechanism.

Figure 19 shows a plot of the HZ field versus radius from the probe measurements at the time of rst bounce. 'I'he agreement between theory and experiment is a remarkable confirmation of the external conductivity theory, because it verifies a case where an externally-trapped axial field is compressed by a factor of 30 to 50. The expected dip in HZ at the axis is not observed because of the -poor spatial resolution of the probe due to the small dimensions involved.

A toroidal pinch tube assembly 200 termed gamma pinch and illustrated in Figures 20-22 of the drawing is also suitable for operationin accordance with the invention. Assembly 200 includes a toroidal pinch tube 201 formed of generally similar semi-circular porcelain or ceramic halves 202 and 203 having terminal flanges, 204, 206 and 207, 208, respectively, disposed in abutting position across sealing IO-rings 209 defining a toroidal vacuum chamber 211 therein and secured as by means of flange bolts (not shown). To the exterior surface of the wall of tube sections 202 and 203 a stabilizing conducting shell 212 formed of metal foil or plating, e.g., (1015-0020 mil copper or silver, is applied. The portions of shell 212 are joined across flanges 2.06 and 208 and left unjoined across flanges 204 and 207, providing a diametricall planar gap 213 thereacross and a longitudinal gap 214 is provided around the inner periphery of shell 212 to permit magnetic field penetration. The stabilizing function of shell 212 was disclosed in the aforesaid copending application as discussed above.

An insulated solenoidal winding 216 disposed concen- 17 trically about tube half-section 202 and a similar winding 217 is employed to provide stabilizing HZ field and for providing the programmed iield as described hereinafter. Such solenoids are constructed to provide a continuous axial symmetrical eld in chamber 211 and are usually energized in a parallel circuit. A single turn primarily 218 constructed of semicircular halves 219V and 221 having terminal anges 222-223 and 224-226 arranged in abutting relation across insulator separators 227 and 228, respectively, is constructed and arranged to encase at least the upper, lower and outer sides of tube 201, with a gap 229 extending around the inner periphery. Primary 218 is conveniently constructed with a rectangular cross seccipally through windings 216 and l217 to very rapidly tion of semiannular upper and lower side sections welded e at the outer periphery to a semicircular hoop section. Reenforcing anges 231 are provided (to prevent movement or collapse of the primary shell on application of intense currents due to associated magnetic fields. Laminated iron cores (not shown) may also be provided encircling primary 218 between said llanges 231. VA most advantageous feature of the foregoing arrangement is inthe large separation permitted between shell 218 and tube 201 by disposing stabilizing shell 212 as indicated thereby obtaining effectively a very thin separation of the initial plasma column from a stabilizing conductor and minimizing the amount of Hz flux remaining exterior Vto the plasma. This result is quite surprising since it was originally thought that the entire primary should be so located to obtain this effect. The terminal flanges 222, 223, 224 and 226 are extended outwardly to provide terminals to which power supply transmission lines may be attached as described below.

Spark plasma sources 232 and 233 are employed in tube sections 202 and 203 to provide initial ionization as above.

Such sources may be constructed as a pair of insulated spaced tungsten electrodes sealed in the tube wall and terminating just inside the tube. RP excitingsolenoid may be employed likewise. Conduit 234 and conduit 236 are connected to gas supply and evacuation pump means (not shown) to supply the desired gas pressure in chamber 211.

Circuitry employed with the toroidal pinch tube apparatus is illustrated in Figure 23 of the drawing. Similar capacitor banks 225 and 230 supplied with charging power as described above are switched in series across terminal iianges 222-224 and 223-226, respectively, of primary 218 to provide the pinch current. More particularly, the positive terminal of bank 225 is coupled to terminal llange 222 and the negative terminall is coupled to the cathode pool 235 of ignitron V240 while the anode 237 is coupled to terminal llange 224 for switching purposes. The cathode pool 238 of ignitron 239 is coupled to ange 224 and the anode 241 to flange terminal 222 for crow-barring as above to permit decay of the field without ringing. Similarly the positive terminal of bank 230 is coupled to flange terminal 226 while the negative terminal is coupled to cathode pool 242 of ignitron 243 and anode 244 is coupled to flange terminal 223 of primary 218. The cathode pool 246 of ignitron 247 is coupled to terminal flange 223 and the anode 248 to ange 226 for crow-barring. Generally speaking, multiple coaxial lines or equivalent low impedance transmission lines are employed vfor such coupling.

Current is supplied to windings 216 and 217 connected in parallel at terminals 249 and 251 so as to provide a continuous axially symmetric HZ eld in chamber 211. More particularly, the positive terminal of a slow capacitor bank 252 is coupled to terminal 249 while vthe negative terminal is coupled to the cathode pool 253 of ignitron 254 and the anode 256'to terminal 251 of the Hz winding to provide vthe initial HZ energizing current. Y A fast capacitor bank 257 employed for programming the Hz eld Iis arranged with the negative terminal coupled to terminal 249 and the positive terminal to the program the HZ field. The high inductance in the circuit of bank 252 thereby prevents aserious -back' current How therethrough. Y v Y v Subsequent to providing the atmosphere, e.g., hydrogen or deuterium'in chamberV 211 operation is synchronized by an initiatingk pulse fromV a multiple channel simultaneous pulse generator 262 `fedthrough one channel of a dual channel time delay unit 2,63 and a Ychannel'of program pu1ser264 to igniter 266 of ignitron 254 which discharges bank 252 through the H7Y winding. As` bank 252 is discharging a pulse fed from unit 262, through lappropriately set time delay unit 267 is applied 1to trigger pulser 268 causing'an ionized plasma to be produced by triggers 232 and 233, coupled thereto, constrained with? in the axially symmetric magnetic field in chamber 211. Immediately, thereafter, the initiating pulse from-,unit 262, fed through dual channel delay unitV 269"and dual channel pulser 271 is applied simultaneouslyto'igniters 272 and 273 of ignitrons 240 and 243, respectivelyfdisfchargingbanks 225 and 230 through primary 218, to .pro- Vide the pinch discharge. As the pinch current nearsr the peak, the initiating pulse from unit 262 applied through dual channel timedelay 274 and crowbarepulser A276 is applied simultaneously to igniters 277 and 278 ofig- -nitrons 239 and l247 to crowbar the pinch circuitand allow the field Vto decay as l/ e. As the pinchftlisclrargel produced thereby moves inwardly, from the wall ofV chamber 211, trapping initial HZ therein, the initiating pulse from unit 262 fed through the second channel'of delay unit 263 and the programmed channel of pulser 264 is applied to the igniter 279 discharging fastcapacitor'bank 257 through the I -IZ winding diminishing or reversing the HZ flux external of the plasma as determined so as to `Vimprove the boundary separation between H, and lHZ or to trap at least one additional Hz peakpexternal to the main plasma column. l p 'r An apparatus wherein the toroidal tube was'of ceramic with a 3/16 thick wall, 4 inches in tubular diameter and 24 inches mean major diameter wasl operatedl as de-V scribed. Thecapacitor `banks powering the pinch tube wereofpidentical joule, 20 kilovolt nominal rating, i.e., 60 capacitors each of 7.5 mfd. capacity usually charged to 1A to 1/2 voltage rating giving about 20 to 30 kilovolts across the primary. Multiple/y paralleled ignitrons were used to carry the heavy currents and the pinch current generally was in the 200,000-3-00,000 ampere range with a scanty laminated core in place. 'I'he slow condenser bank provided the initial eld lin millisecond or somewhat less time period while the fast condenser bank was capable of producing etective .bucking ou or reversing fields inv microseconds. Hz winding had 16 turns, slow bank of 6() capacitors of 7.5. mfd. charged to about 5000 volts and the fast bank 1Z0-7.5 mfd. capacitors charged to 10.5 kilovolts nominal rating but voltages adjusted to give the desired method of oper# ation. The primary conductor was fabricated of aluminum heliarc welded.

In atypical sequence of operations the slow bank was red to produce the initial stabilizing HZ eld in" the Vacuum chamber. After times of from about 50-150 microseconds the triggers were tired providing initial yionization and trapping a relatively cool plasma retainedin the I -IZ iield in the chamber. At about 200,microseconds the pinch current was applied requiring about 14 seconds to reach peak and was crow-barred to decay to 1/e in about 15 nseconds. At times of about 2-3 seconds following application of the pinch current when the pinch discharge was formed or was moving inwardly the fast reversing bank was discharged to reduce, reverse or otherwise program Hz field external to the pinch. Initial deuterium pressures of 5 to 20 microns were employed resulting in the production of neutrons under various operating conditions.

The neutron production dependence on HZ field program is quite distinctive with the various modes of operation. If an initial HZ field of 1600 gauss was employed and was compressed simply by application of the pinch field the indistinct distribution illustrated in Figure 24 of the drawing was obtained and the neutron production was low or absent. If the fast Ireversing bank was employed to reduce external Hz to zero or slightly below, the pinch distribution becomes sharp as illustrated in Figure 25. Iff a considerable excess of reverse or negative Hz was programmed into `the plasma external to the pinch the neutron yield became larger as indicated in Figure 26 of the drawing. Preliminary considerations indicate that temperatures of the order of 50 e.v. have been obtained with higher temperatures obtainable in larger apparatus and with additional care being given to excluding extraneous wall materials and other impurities which cool the plasma by increasing radiation losses. Neutron yields equivalent to about 500 e.v. have been observed.

While there have been described in the foregoing what maybe considered to be preferred embodiments of the invention modification may be made therein without departing from the teachings of the invention and it is intended to cover all such as fall within the scope of the appended claims.

What we claim is:

1. Apparatus for the production and manipulation of a plasma comprising electrical gaseous pinch discharge tube means provided with evacuation and -gas supply means for introducing a gaseous atmosphere therein, means for supplying an initial axially symmetric stabilizing HZ field in said discharge tube, electrical power supply means for initiating and establishing the gaseous pinch discharge in said tube thereby providing a plasma in which said initial stabilizing HZ field is trapped and the plasma is compressed leaving a residual portion of the Hz field in the plasma external to the main plasma column, and axially symmetric magnetic field generating means coupled to said tube and programmed as a function of said compression for supplying magnetic field to said tube to modify the boundary value of said external Hz field.

2. Apparatus for the production of a stabilized pinch discharge comprising a pinch discharge tube provided with evacuation and gas supply means for introducing a gaseous atmosphere therein, a solenoid disposed to provide an axially symmetric HZ eld within said tube, electrical power supply means adapted to supply an energizing current to said solenoid to produce an initial stabilizing I-lz field therein, electrical power supply means coupled to said tube to initiate and produce a pinch discharge in said -tube whereby the major proportion of said HZ field is trapped in the plasma and is compressed therewith leaving a residual amount of Hz field external thereto, and electrical power supply means having the output programmed as a function of said compression and with the programmed current output applied to said solenoid to modify the wall boundary value of the external HZ field and thereby modify the boundary value of the I-IZ and H, fields of the pinch discharge.

3. Apparatus as defined in claim 2 wherein said discharge tube is provided with means for producing an initial ionized plasma in said initial stabilizing Hz field.

4. Apparatus `for the production of a stabilized pinch discharge comprising a discharge tube including a tubular housing defining a Chamber provided with longitudinally spaced electrodes and fitted with evacuation and gas supply means for introducing a gaseous atmosphere into said chamber, -a solenoidal winding disposed to provide an axially symmetric HZ field in said chamber, electrical power supply means arranged to applyvcurrent to said solenoidal winding to establish an initial HZ field therein, electrical power supply means connected to said electrodes to produce Ia pinch discharge which traps and compresses the H. field in the plasma in the chamber with a residual portion remaining external thereto, and electrical power supply means having the current output programmed as a function of said compression said programmed current output being applied to said solenoid to modify the wall boundary value of the external Hz field and thereby modify the boundary value of the I-IZ and He fields of the pinch discharge.

5. Apparatus for the production of a stabilized pinch discharge comprising a discharge tube including a tubular housing defining a chamber provided with longitudinally spaced electrodes and with the split cylindrical return conductor of one 9i said electrodes extending along said housing said tubebeing fitted with evacuation and gas supply means for introducingl a gaseous atmosphere into said chamber, a solenoidal winding disposed exteriorly of said return conductor to provide an axially symmetric Hz field in said chamber, a programmed Hz eld solenoid disposed between said return conductor and the tube Wall, electrical power supply means arranged to apply current to said solenoidal windingto establish an initial Hz field therein, electrical power supply means connected to said electrodes to produce a pinch discharge which traps and compresses the HZ field in the plasma in the chamber with a residual portion remaining external thereto, and electrical power supply means having the current output programmed as a function of said compression said programmed current output being applied to said programmed HZ field solenoid to modify the wall boundary value of the external HZ field and thereby modify the boundary value of the HZ and I-l6 fields of the pinch discharge.

46. Apparatus for the production of a stabilized pinch discharge comprising a discharge tube including a tubular insulator housing defining a chamber having electrodes disposed terminally therein and with the split cylindrical return conductor of the second of said electrodes disposed along said housing said tube being fitted with evacuation and gas supply means for introducing a gaseous atmosphere in said chamber, an HZ solenoidal winding disposed concentrically about said return conductor, a programmed Hz field solenoid disposed between said return conductor land the tube wall, electrical power supply means arranged to apply current to said solenoidal winding to establish an initial axially symmetric HZ field in said chamber, electrical power supply means connected to the rst electrode and return conductor of the second electrode of said tube to produce a pinch discharge which traps and compresses the HZ field in the plasma in the chamber with a residual portion remaining external thereto, a capacitor coupled across said programmed HZ field coil which produces an oscillation therein on establishment of the pinch discharge effective in modifying the wall boundary value of the Hz field so` as to trap at4 least one additional I-IZ field peak in the external plasma region.

7. Apparatus for the production of a stabilized pinch discharge comprising a discharge tube including a tubular insulator housing defining a chamber having electrodes disposed terminally therein and with -the split cylindrical return conductor of the second of said electrodes disposed along said housing said tube being fitted with evacuation and gas supply meansr for introducing a gaseous atmosphere into said chamber, an Hz solenoidal winding disposed concentrically about said return conductor, a programmed HZ field solenoid disposed lbetween said return conductor and the tube wall, electrical power Supply means arranged to apply current to said solenoidal Wind- 

